1. Field of the Invention
This invention generally relates to the field of encoding and decoding hidden data in electronic signals. More particularly, the present invention relates to a system and method for enabling a user to retrieve, decode, and utilize hidden data embedded in audio signals.
2. Description of Related Art
Generally, technology for embedding hidden data in electronic signals is well known in the art. One such technology is known as digital watermarking. Digital watermarking technology has developed along with the need to devise more effective ways for protecting copyrights of images and music made available to the public through the Internet.
In digital watermarking, a watermark is embedded in spectral components of a data signal using, for example, spread spectrum techniques. This watermark, which is actually hidden information streams, is primarily used to protect against illegal use of proprietary images and/or music produced in the form of electronic signals. The watermark is virtually impossible to remove and is integrated throughout the signal. Digital watermarking is therefore particularly effective for protecting and tracking the use of electronic images and music. Although the watermark is not perceptible to human senses, it can be detected electronically using a variety of different detection and retrieval techniques. One particularly beneficial use of this technology is the ability to watermark audio signals. In this capacity, watermarks can be used by commercial industry, for example, to protect against the illegal use of copyright protected songs or to monitor the use and broadcast of commercials.
In traditional applications of watermarking, watermarks are added to a piece of music, or a commercial, for example, at various points in the recording and/or distribution cycle. In a song, a watermark might be added at the studio and may contain the name of the studio, date and names of the musicians, and their copyright statement. Another watermark may be added by the record company, containing their copyright statement, when a compact disk (CD) is created. Finally, another watermark could be added by the radio station when the CD or commercial is played and broadcast. Although inaudible to the listener, the virtually indestructible watermark remains in the audio associated audio signal. That is, the watermark remains embedded in the electronic version of the song or commercial.
At any point where a user can hear the music, such as when the music is reproduced through an audio speaker, the listener would be able to decode the embedded watermark with the proper equipment. In the case of broadcast music, the decoded watermark could provide the user with the name of a particular song, and the name of the record company. The watermark could also provide the call letters of the radio station and any other information added to the watermark along the recording and/or distribution cycle of the associated audio signal. The ability to decode watermarks in this manner also provides a means to monitor the use, and/or amount of airplay of materials such as radio commercials.
As mentioned above, techniques for embedding hidden information in data signals are well known in the art. For example, U.S. Pat. No. 5,822,360, issued to Lee et al. on Oct. 13, 1998 describes one such method. In Lee, auxiliary data is transported in an audio signal by hiding the data in the form of colored noise. Colored noise has a signal spectrum similar to the audio signals. Thus, the auxiliary data is first converted to a spread spectrum signal and the resulting audio signal is analyzed to determine its spectral shape. The same spectral shape is then imparted to the spread spectrum signal, which is combined with the audio signal for transmission. The spectral shaping can be performed using techniques such as linear predictive coding or sub-band coding techniques such as fast Fourier transforms.
Another technique for embedding a watermark in a signal is disclosed in U.S. Pat. No. 5,905,800, issued to Moskowitz et al. on May 18, 1999. In Moskowitz, first a watermark key is identified. The key includes a binary sequence and information describing application of the binary sequence to the signal. The digital watermark is then encoded within the content signal at one or more locations by the watermarking key.
Similarly, a number of prior art approaches are available for decoding an embedded watermark from an audio signal. One technique requires the audio signal to first be broadcast through an audio speaker, such as a radio speaker, in the form of sound waves. Since the watermark is inaudible to humans, a microphone is used to receive the associated sound waves and convert the received sound waves into an electrical signal. Next, the electrical signal is analyzed, using prior art signal processing techniques, in order to locate and decode the watermark and retrieve the information embedded therein. As mentioned above, the information could be the name of a song, the name of an associated record company, the call letters of the radio station, information regarding a broadcast commercial, and/or any other type of information.
Given the increased dependence on wireless communications, there is a need to integrate the use of digital watermarking into the wireless communications arena. In this regard, there is also a need for a system and method that provides a user with the ability to detect and decode a watermark and/or other information hidden in an audio signal and present the decoded information to an end user.